The present invention relates to a fuel injector with electromagnetic actuation of the plunger.
An electromagnetic fuel injector normally comprises a tubular supporting body with a central channel which performs the function of a fuel duct and ends in an injection jet regulated by an injection valve controlled by an electromagnetic actuator. The injection valve is provided with a plunger, which is rigidly connected to a mobile armature of the electromagnetic actuator so as to be displaced by the action of the electromagnetic actuator between a closed position and an open position of the injection jet against the action of a spring, which tends to hold the plunger in the closed position.
One example of an electromagnetic fuel injector of the above-described type is given in U.S. Pat. No. 6,027,050-A1, which relates to a fuel injector provided with a plunger that, at one end, co-operates with a valve seat and at the opposite end is integral with a mobile armature of an electromagnetic actuator; the plunger is guided at the top by the armature and is guided at the bottom by sliding of the end portion of the plunger in a guide portion of the valve seat.
Known electromagnetic fuel injectors of the above-described type are very widely used because they combine good performance with low cost. However, such injectors with electromagnetic actuation of the plunger are not capable of operating at very high fuel pressures; it is for this reason that injectors with hydraulic actuation of the plunger have been proposed, i.e. injectors in which displacement of the plunger from the closed position to the open position against the action of the spring proceeds under the effect of hydraulically generated forces. One example of an injector with hydraulic actuation of the plunger is provided by patent applications EP-1036932-A2 and EP-0921302-A2; a further example of an injector with hydraulic actuation of the plunger is provided by patent application WO-0129395-A1.
Injectors with hydraulic actuation of the plunger exhibit good dynamic performance and are capable of operating at very high fuel pressures. However, such injectors are complex and costly to produce because they require the provision of a hydraulic circuit having a piezoelectrically or electromagnetically actuated control valve. Moreover, in an injector with hydraulic actuation of the plunger, there is always a certain degree of backflow of fuel, which is discharged at ambient pressure; such fuel backflow has two negative effects in that it wastes energy and tends to heat up the fuel. Finally, in an injector with hydraulic actuation of the plunger, there is a substantial drop in fuel pressure due to the load losses brought about by the injector itself; by way of example, if the fuel is supplied to an injector with hydraulic actuation of the plunger at an inlet pressure of 120 MPa, there may be load losses of up to 20 MPa brought about by the injector, such that the effective injection pressure of the fuel is 100 MPa.
US2003201346 discloses A fuel injection valve, which has an electromagnetic coil using an insulated coil wire covered with an insulating coating and having a fusion bonding layer with self-fusing properties coated over the insulating coating; therefore, it is possible to dispense with the use of a bobbin and hence possible to provide a low-cost and compact fuel injection valve that requires a reduced number of man-hours for production. Further, a flaw or a pinhole in the insulating coating is repaired by self-fusion, and thus insulation properties and waterproofness are improved; accordingly, it is possible to prevent disconnection of the coil due to electrolytic corrosion.